Electrical plug and receptacle



' Oct. 24, 1967 E. GRANTZ 3,349,360

ELECTRICAL PLUG AND RECEPTACLE Filed March 24, 1966 mm gm I/VVENTOR. EL 5 K GRANTZ United States Patent Oflice 3,349,360 ELECTRICAL PLUG AND RECEPTACLE Elek Grantz, 107 Crystal Ave, Lombard, Iii. 60148 Filed Mar. 24, 1966, Ser. No. 537,233 Claims. (Cl. 33-14) This invention relates to electrical grounding means for a two prong lug and two terminal receptacle to form a third prong and third terminal.

Safe use of electric power tools and appliances of all kinds has been stressed by Safety Councils for years. Many power tools and appliances are sold and have been sold without incorporating a positive third wire ground to prevent electrical shocks being transmitted to the person using the tools or appliances.

Power tools and ap liances are, of course, manufactured and sold with a three wire cord. The two main wires of such a cord are for attachment to a pair of spaced, parallel outwardly extending, flat prongs on the connector-plug with a third wire attached to a usually differently-shaped third prong on the connector-plug. Obviously, the use of this type of plug requires a three terminal receptacle. However, to make possible the use of a three wire cord and appropriate plug with a two terminal receptacle requires an adaptor. The adaptor is rovided with a pair of prongs for engagement in the normal two-terminal receptacle. The other end of the auxiliary plug is formed with a pair of flat, parallel slots aligned with the pair of prongs. In'addition, this other end of the auxiliary plug has a third opening formed therein to accommodate the third prong on a three prong plug. Such adaptor also has a supplemental Wire leading out from the side thereof. The inner end of the wire is attached to a contact embedded in the plug at the end of the opening which accommodates the third prong. The free end of the wire has secured thereto a bifurcated clip which is adapted for seating under the screw which secures the face or closure-plate to the electric box. Such an auxiliary plug makes possible the connection of a three-wire plug to a two-terminal wall receptacle with the three wire plug grounded to the terminal box. However, the average person usually fails or forgets to make such connection for the ground wire being indifierent about his safety. It was to overcome this inconvenience of the adaptor plug the present invention was conceived.

The main objects of this invention are: to provide an im roved structuring of a three-prong terminal plug for use with three-wire electrical cord; to provide an improved and simple means for converting or producing a convenional two-prong plug for use with three-wire cord; to provide two specially formed elements adapted for attachment, respectively, to a two-prong plug and a two terminal receptacle box to ground a three-wire cord to a standard two-prong plug; and to provide two such elements of this kind of such simple and practical form as to make simple and inex ensive and manufacturing and marketing thereof either as permanent parts of a twoprong plug or for facile use to convert a conventional two-prong plug for use with a three-wire cord to permit grounding thereof to a terminal box.

One specific embodiment of this invention is shown in the accompanying drawings, in which:

FIG. 1 is a front view of a conventional, double or dual outlet receptacle mounted in a wall-recessed receptacle box and covering plate with the spring clip of the present invention;

FIG. 2 is a vertical sectional view of the same taken on the plane of the line 2-2 of FIG. 1 showing secured thereto one half of the spring clip forming a part of this invention;

FIG. 3 is a vertical sectional view taken on the plane Efidhfifid Patented Get. 24, 1967 of the line 3-3 of FIG. 2, but showing the full spring clip of this invention;

FIG. 4 is a side elevational view of a conventional two-prong plug having associated therewith the third prong;

FIG. 5 is an end view taken in the direction of line 55 of FIG. 4;

FIG. 6 is a sectional view of the plug aken on the line 66 of FIG. 5; with the third prong in place;

FIG. 7 is a greatly enlarged elevational view of the auxiliary third prong element constructed in accordance with this invention; and

FIG. 8 is a perspective view of the spring clip for the third prong of the plug for grounding and which is normally adapted for attachment by the screw that holds the cover plate in place on the receptacle unit as shown in FIGS.1, 2 and 3.

The essential concept of this invention involves a pair of complementary elements for converting a two-prong plug for use with a three-wire electric appliance or tool and a two terminal receptacle in a three terminal receptacle cord.

A pair of elements embodying the foregoing concept, for use with a conventional two-prong plug 11, comprises a third prong or a pin element 12 and a clip element 13.

One type of conventional electrical two-prong plug 11, as shown in the accompanying drawing, has a main body part 14 with an axially-disposed integral stem 15. The body part 14 has the usual recess 16 extending inwardly from a fiat, end face 17 and communicating with an axial bore 18 in the stern part 15. A plug 11 of this kind often is molded rubber or a rubber-like composition of quite stable character and/ or any ofthe plastics which are not electrically conductive. As herein shown, a portion of the body part 14 has a fiat peripheral portion 19. Such a plug may be so formed in its production or one may have a portion cut away to form such a flat portion 19.

The recess 16 here is shown as of considerable depth and seats the usual fiber ring 21 which is pressure fitted therein. A pair of metal contacts 22, generally L-shaped each with an arcuately-formed base 23 and an integrated right-angle prong 24, are secured to the fiber ring 21 by screws 25 and positioned with the prongs 24 in spaced parallel relationship in the usual and normal manner.

A small bore 26 (FIGS. 5 and 6) extends inwardly into and communicates with the recess 16 from the fiat portion 19 of the plug 11 for the reception of a pin 12 which is to be secured in place by a screw 37 to the fiber ring 21.

A three wire electric cord 28 extends in through the bore 18 and has the stripped ends of the two main wires (not shown) secured to the respective contacts 24 by screws 25. The third or ground wire is secured to the pin 12 under the screw 27.

Such a two-prong plug 11 is structured for use with the usual two-terminal receptacle 29. Two such receptacles are shown exposed through openings in a closure or face plate 30, for a conventional, wall-recessed electric box 31. The plate 30 is secured in position by a screw 32 threaded on a conventional metal bracket (not shown) of the receptacle 29.

The pin 12, as shown greatly enlarged in FIG. 7, has a flattened end 34 with an aperture 35. To complete a plug 11 for use with a three-wire cord, the pin 12 is seated in the aperture 26 as shown in FIGS. 5 and 6. This is elfected by pressing the small end inwardly from the recess 16 and through the bore 26 until the aperture 35 is aligned for the reception of the screw 27, as shown in FIG. 6.

The clip 13 is formed into U-shape from a strip of thin spring-metal. Portions of the parallel parts of the strip may be folded back inwardly towards each leg to form slightly restricted openings 36 (FIGS. 3 and 8). The base 37 of the clip 13 has an aperture to permit inserting the face plate screw 32 to secure the clip 13 to the plate 30 to position the clip 13 outwardly above the plate 30 and so that when the plug 11 is pressed into one pair of the appropriate terminals in the receptacle 29 the pin 12 will automatically enter the clip 13 and ground the third wire of the three-wire cord to the terminal box 31.

Although but one specific embodiment of this invention is herein shown and described, it will be understood that numerous details of the construction shown may be altered or omitted without departing from the spirit of the invention as defined by the following claims.

I claim:

1. A device of the class described comprising an electrical plug recessed inwardly from one end and having a bore extending therethrough for the insertion of a threewire electric cord, a pair of parallel terminal contacts fixed in the recessed end of the plug and extending axially outwardly therefrom in spaced, parallel, axial relationship, a first element fixed on the plug with a portion thereof extending radially outward therefrom, a second element apertured for attachment to the face plate of a wallmounted receptacle and positioned for automatic embracing contact with the first element when the prongs on the plug are inserted into the receptacle.

2. The device set forth in claim 1 wherein the first element is in the form of a pin with a flat apertured inner end to secure said element to the plug, and the second element is a strip of spring metal of U-shape with the base apertured for attachment to the box and positioned on the closure plate by the screw that secures the plate to the box.

3. The device set forth in claim 2 wherein the ends of the parallel parts of the spring clip are doubled back upon themselves to form rounded knob contacts for the reception of the exposed end of the pin.

4. In a device of the class described, a pair of separately-for'med elements for converting a conventional electrical plug, having a recessed end and a pair of prongs extending axially outwardly therefrom, for use with a three-wire cord; and a two slot electric receptacle, one of the elements being a pin of a length and one-end form to permit its insertion radially into the plug and anchoring the one end of the pin in the plug recess to constitute a third terminal with the opposite end of the pin extending outwardly of the plug periphery and lying in a plane normal to the axis of the plug, and said pair of prongs, the other element comprising a spring metal clip electrically grounded to a closure plate for a wall-recessed receptacle and dispose the other end of the clip for contact with the exposed end of the pin when the plug is seated in the receptacle.

5. A device according to claim 4 wherein the other element is U-shaped with an aperture in the base thereof and the ends of the parallel parts bent inwardly to form a restricted opening for automatically engaging the exposed end of the pin.

References Cited UNITED STATES PATENTS 2,484,558 10/1949 Eisner 339-14 FGREIGN PATENTS 603,866 8/1960 Canada. 1,271,165 7/1961 France.

MARViN A. CHAMPION, Primary Examiner.

PATRICK A. CLIFFORD, Examiner. 

1. A DEVICE OF THE CLASS DESCRIBED COMPRISING AN ELECTRICAL PLUG RECESSES INWARDLY FROM ONE END AND HAVING A BORE EXTENDING THERETHROUGH FOR THE INSERTION OF A THREEWIRE ELECTRIC CORD, A PAIR OF PARALLEL TERMINAL CONTACTS FIXED IN THE RECESSED END OF THE PLUG AND EXTENDING AXIALLY OUTWARDLY THEREFROM IN SPACED, PARALLEL, AXIAL RELATIONSHIP, A FIRST ELEMENT FIXED ON THE PLUG WITH A PORTION THEREOF EXTENDING RADIALLY OUTWARD THEREFROM, A SECOND ELEMENT APERTURED FOR ATTACHMENT TO THE FACE PLATE OF A WALLMOUNTED RECEPTACLE AND POSITIONED FOR AUTOMATIC EMBRACING CONTACT WITH THE FIRST ELEMENT WHEN THE PRONGS ON THE PLUG ARE INSERTED INTO THE RECEPTACLE. 